JP6471700B2 - Method for melting silicon raw material using recharge device - Google Patents

Description

  The present invention relates to a silicon raw material recharging device used in a silicon single crystal manufacturing process by the Czochralski method (hereinafter referred to as CZ method) and a silicon raw material melting method using the recharging device.

  A multiple pulling method is known as a method for producing a silicon single crystal by the CZ method (see, for example, Patent Document 1). In the multiple pulling method, after pulling up the silicon single crystal, additional raw materials such as polycrystalline silicon are melted in the same quartz crucible, and the silicon single crystal is pulled up from the obtained silicon melt. By repeating the raw material supply step and the single crystal pulling step, a plurality of silicon single crystal ingots are manufactured from one quartz crucible. According to the multiple pulling method, the manufacturing cost per single crystal ingot including the cost of the quartz crucible can be reduced. In addition, since the frequency with which the chamber is disassembled and the quartz crucible is replaced can be reduced, it is possible to improve operational efficiency.

  In the multiple pulling method, a recharging device which is a tool for additionally supplying raw materials is used. For example, Patent Document 1 describes a recharging device in which a double plate type bottom plate is provided at the lower end of a cylinder made of quartz, and the bottom plate is made of molybdenum. The cylindrical body containing the lamp-shaped raw material is placed above the crucible in the chamber in a state where it is suspended by a wire, and the bottom plate is opened, whereby the lamp-shaped raw material is put into the crucible.

  Patent Document 2 discloses a recharging device including a cylindrical hopper body made of quartz glass and a bottom lid that opens and closes a lower end opening of the hopper body. The bottom lid has a conical shape and includes bubbles. It is described that it consists of quartz glass.

  As a method for melting the raw material in the quartz crucible, for example, in Patent Document 3, in order to reduce heat loss when the raw material is melted, the raw material is placed in a state where a heat shielding plate (melt lid) is installed so as to cover the upper part of the crucible. A method of melting is described.

JP 57-95891 A JP 2004-244236 A JP-A-3-193694

  In the melting step of the silicon raw material, when the above-described melt lid is used, the heating efficiency of the raw material can be increased, and thereby a certain power reduction effect can be expected.

  However, when using the above-described recharge device and melt lid, after the raw material is additionally charged using the recharge device, the material melting step must be performed after the recharge device is taken out of the chamber and replaced with the melt lid. However, since it is necessary to increase the power of the heater during the replacement process in order to suppress a decrease in the temperature in the chamber, there is a problem that an expected power reduction effect cannot be obtained.

  Accordingly, an object of the present invention is to provide a recharging apparatus that can not only reliably recharge a raw material but also increase the heating efficiency of the raw material in the subsequent raw material melting step. Another object of the present invention is to provide a silicon raw material melting method having a high power reduction effect using such a recharging device.

  In order to solve the above problems, a recharging apparatus according to the present invention includes a charge pipe that stores a silicon raw material, a bottom lid that opens and closes a lower end opening of the charge pipe, and a shaft that supports the bottom lid to be movable up and down. The bottom cover includes a cone-shaped cone portion constituting the inner bottom surface of the charge tube and a flat bottom plate portion constituting the outer bottom surface of the charge tube, and the cone portion is made of quartz glass, The bottom plate portion is made of a material having higher heat resistance than the cone portion, and the bottom cover opens the lower end opening by descending below the lower end opening to open the silicon raw material in the charge pipe It is characterized by dropping.

  According to the present invention, the heat resistance of the bottom cover can be enhanced while ensuring the prevention of contamination of the silicon raw material accommodated in the charge tube and the ease of taking it out. Therefore, the bottom lid can be used as a melt lid at the time of melting the raw material, and the heating efficiency of the raw material by heating the raw material while using the bottom lid as the melt lid in the melting process of the silicon raw material recharged in the quartz crucible. The power consumption can be reduced and the raw material melting time can be shortened.

  In the present invention, the bottom plate portion preferably includes at least one material selected from graphite, tungsten, and molybdenum. When the bottom plate portion is made of any of these materials, the heat resistance of the bottom plate portion can be increased, and thus the bottom lid can be used as a melt lid.

  In the present invention, the inside of the bottom lid surrounded by the cone portion and the bottom plate portion may be a cavity, and the inside of the bottom lid may be filled with carbon fiber. When the carbon fiber is filled, the heat resistance of the bottom cover can be further increased.

  In the present invention, a multilayer structure in which a heat insulating material layer and a hollow layer are alternately stacked is provided inside the bottom lid surrounded by the cone portion and the bottom plate portion, and the heat insulating material layer is It is preferable to contain at least one material selected from graphite, tungsten and molybdenum. According to this structure, the heat resistance of the bottom lid can be further increased.

  In the present invention, a multilayer structure in which first heat insulating material layers and second heat insulating material layers are alternately stacked is provided inside the bottom lid surrounded by the cone portion and the bottom plate portion. The first heat insulating material layer preferably includes at least one material selected from graphite, tungsten, and molybdenum, and the second heat insulating material layer is preferably made of carbon fiber. According to this structure, the heat resistance of the bottom lid can be further increased.

  Further, the silicon raw material melting method according to the present invention using the recharge device includes a step of disposing the recharge device containing the silicon raw material above a quartz crucible in a chamber, and a lower end of the charge tube of the recharge device. A step of lowering the bottom lid closing the opening to recharge the silicon raw material in the charge tube into the quartz crucible; and a state in which the recharge device is installed in the chamber and the bottom lid is lowered. And the step of heating and melting the silicon raw material in the quartz crucible with a heater.

  As described above, the silicon raw material melting method according to the present invention heats the raw material while using the bottom cover of the recharge device as a melt lid in the melting step of the recharge raw material, thereby increasing the heating efficiency of the raw material and reducing the power consumption. In addition, the setup loss from the recharging device to the melt lid can be reduced.

  Furthermore, the method for producing a silicon single crystal according to the present invention using the recharge device includes a step of disposing the recharge device containing a silicon raw material above a quartz crucible in a chamber, and the charge tube of the recharge device. Lowering the bottom lid that closes the lower end opening of the battery to recharge the silicon raw material in the charge tube into the quartz crucible, and the recharge device is installed in the chamber and the bottom lid is lowered. The silicon raw material in the quartz crucible in a state is heated and melted by a heater, and the silicon single crystal is pulled from the silicon melt in the quartz crucible.

  As described above, the silicon single crystal manufacturing method according to the present invention heats the raw material while using the bottom lid of the recharge device as a melt lid in the melting step of the recharge raw material, thereby increasing the heating efficiency of the raw material and reducing power consumption. Not only can this be done, but the setup loss from the recharging device to the melt lid can be reduced.

  According to the present invention, it is possible to provide a recharging device that can not only reliably recharge a raw material but also increase the heating efficiency of the raw material in the subsequent raw material melting step. In addition, according to the present invention, it is possible to provide a silicon raw material melting method having a high power reduction effect using such a recharging device.

FIG. 1 is a schematic cross-sectional view showing the configuration of a silicon single crystal manufacturing apparatus to which a recharging apparatus according to the present invention is applied. 2 (a) and 2 (b) are schematic cross-sectional views showing the configuration of the recharging device according to the embodiment of the present invention, in which (a) is a state in which the bottom cover is closed and a silicon raw material is accommodated. b) shows a state where the bottom lid is opened and no silicon raw material is accommodated. FIG. 3 is a schematic cross-sectional view for explaining a silicon material recharging step and a melting step using the recharging device. FIG. 4 is a schematic cross-sectional view for explaining a silicon material recharging step and a melting step using a recharging device. FIG. 5 is a schematic cross-sectional view for explaining a silicon material recharging step and a melting step using a recharging device. FIG. 6 is a schematic cross-sectional view for explaining a silicon material recharging step and a melting step using a recharging device. FIGS. 7A to 7C are graphs showing simulation results of power consumption for one recharge raw material. 8A to 8D are cross-sectional views showing variations of the structure of the bottom cover of the recharging device.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic cross-sectional view showing the configuration of a silicon single crystal manufacturing apparatus to which a recharging apparatus according to the present invention is applied.

  As shown in FIG. 1, the silicon single crystal manufacturing apparatus 1 includes a chamber 10, a heat insulating material 11 disposed along the inner surface of the chamber 10, a quartz crucible 12 that supports the silicon melt 3 in the chamber 10, A graphite crucible 13 that supports the quartz crucible 12, a shaft 14 that supports the graphite crucible 13, a heater 15 disposed around the graphite crucible 13, a heat shield 16 disposed above the quartz crucible 12, and graphite A single crystal pulling wire 17 disposed above the crucible 13 and coaxially with the shaft 14 and a wire winding mechanism 18 disposed above the chamber 10 are provided.

  The chamber 10 includes a main chamber 10a and an elongated cylindrical pull chamber 10b connected to the upper opening of the main chamber 10a. The quartz crucible 12, the graphite crucible 13, the heater 15 and the heat shield 16 are the main ones. It is provided in the chamber 10a. The pull chamber 10b is provided with an introduction port 10c for argon gas (purge gas), and an exhaust port 10d for argon gas is provided at the bottom of the main chamber 10a. A flow of argon gas is generated in the chamber 10 from the upper side to the lower side. Furthermore, a locking piece 10e is provided inside the pull chamber 10b to limit the lowering operation of the recharging device described later.

  The quartz crucible 12 is a quartz glass container having a cylindrical side wall and a curved bottom. A graphite crucible 13 that supports the quartz crucible 12 is connected to the upper end of a shaft 14 that extends in the vertical direction. The lower end of the shaft 14 penetrates the center of the bottom of the chamber 10 and is a shaft drive provided outside the chamber 10. It is connected to the mechanism 19.

  The heater 15 is used for melting the silicon raw material filled in the quartz crucible 12 to generate the silicon melt 3. The heater 15 is a carbon resistance heating heater, and is arranged concentrically outside the graphite crucible 13.

  The heat shield 16 is provided to prevent heating of the single crystal 2 due to radiant heat from the heater 15 and the quartz crucible 12 and to suppress temperature fluctuation of the silicon melt 3. It is preferable to use graphite as the material of the heat shield 16. The heat shield 16 is a member having an inverted truncated cone shape whose diameter is reduced from the upper side to the lower side, and is provided so as to cover the upper part of the silicon melt 3 and to surround the growing single crystal 2. Since the lower end portion of the heat shield 16 is located inside the quartz crucible 12, it does not interfere with the heat shield 16 even if the quartz crucible 12 is raised. An opening 16a larger than the diameter of the single crystal 2 is provided at the center of the heat shield 16, and the single crystal 2 is pulled upward through the opening 16a.

  The graphite crucible 13, the shaft 14, and the shaft drive mechanism 19 constitute a crucible rotating mechanism that rotates the quartz crucible 12 and a crucible lifting mechanism that lifts and lowers the quartz crucible 12. As the single crystal 2 grows, the amount of melt decreases and the liquid level in the quartz crucible 12 decreases, so that the quartz crucible 12 has a constant distance from the lower end of the heat shield 16 to the melt surface. Control to raise the is performed.

  Above the quartz crucible 12, a wire 17 that is a pulling shaft of the single crystal 2 and a wire winding mechanism 18 that winds the wire 17 are provided. The wire winding mechanism 18 has a function of rotating the single crystal 2 together with the wire 17. The wire winding mechanism 18 is disposed above the pull chamber 10b, the wire 17 extends downward from the wire winding mechanism 18 through the pull chamber 10b, and the tip of the wire 17 is located inside the main chamber 10a. The space has been reached. FIG. 1 shows a state in which the single crystal 2 being grown is suspended from the wire 17. When pulling up the single crystal 2, the seed crystal is immersed in the silicon melt 3, and the single crystal 2 is grown by gradually pulling up the wire 17 while rotating the quartz crucible 12 and the seed crystal, respectively.

  In the single crystal pulling step, seed drawing (necking) is first performed by the dash neck method in order to make the single crystal dislocation-free. Next, in order to obtain a single crystal having a required diameter, a shoulder portion having a gradually widened diameter is grown, and when the single crystal reaches a desired diameter, a body portion having a constant diameter is grown. After growing the body portion to a predetermined length, tail restriction is performed to separate the single crystal from the melt 3 in a dislocation-free state.

  In the multiple pulling method, after pulling up one silicon single crystal ingot, the silicon raw material is recharged and melted in the same quartz crucible 12, and a new silicon single crystal is pulled up from the obtained silicon melt. A plurality of silicon single crystals can be manufactured from one quartz crucible 12 by repeating such a raw material supply step and a single crystal pulling step.

  The recharging of the silicon raw material may be performed not only in the second and subsequent silicon single crystal raw material melting step, but also in the first silicon single crystal raw material melting step. In this case, it may be performed in a so-called single pulling method in which only one silicon single crystal is manufactured from one quartz crucible 12. Usually, in the production of the first silicon single crystal, the initial raw material previously filled in the quartz crucible 12 is heated by a heater and melted. At this time, the volume of the silicon raw material is reduced and a free space is generated in the quartz crucible 12. Here, in order to pull up a single crystal as long as possible, it is necessary that as much silicon material as possible be charged in the quartz crucible 12, and for this reason, the silicon material is recharged in the quartz crucible 12. . The present invention is not limited to the use of recharging the raw material in the multiple pulling method, and may be used for the purpose of recharging the additional raw material when a certain amount of the initial raw material has melted in the so-called single pulling method.

  Next, a recharging device used when recharging silicon raw material in the quartz crucible 12 will be described.

  2 (a) and 2 (b) are schematic cross-sectional views showing the configuration of the recharging device according to the embodiment of the present invention. FIG. 2 (a) shows a state in which the bottom lid is closed and the silicon raw material is accommodated. FIG. 2B shows a state in which the bottom cover is opened and no silicon raw material is accommodated.

  As shown in FIGS. 2 (a) and 2 (b), the recharging device 20 includes a charge pipe 21 that houses a lamp-shaped silicon raw material S, a flange member 22 that closes an upper end opening 21a of the charge pipe 21, A bottom cover 23 that opens and closes a lower end opening 21b of the charge tube 21, a shaft 24 that supports the bottom cover 23, and a guide tube 25 into which the shaft 24 is inserted are provided.

  The charge tube 21 is a cylindrical member made of quartz glass, and its diameter is set to be the same as the diameter of the silicon single crystal to be pulled up, but slightly smaller than that. A through hole 22a is provided at the center of the flange member 22 that closes the upper end opening 21a of the charge pipe 21, and the shaft 24 and the guide pipe 25 are inserted into the charge pipe 21 through the through hole 22a. It reaches the upper end of the bottom lid 23 through the tube 21.

  The bottom cover 23 is a three-dimensional member, and includes a conical cone portion 23 a that forms the inner bottom surface of the charge tube 21 and a flat bottom plate portion 23 b that forms the outer bottom surface of the charge tube 21. In the present embodiment, the bottom lid 23 has a hollow structure, and the space surrounded by the cone portion 23a and the bottom plate portion 23b is a cavity, but may be filled with a heat insulating material.

  The cone portion 23 a is made of quartz glass like the charge tube 21 and plays a role of preventing contamination of the silicon raw material S in the charge tube 21. In addition, an inclined surface is provided for smoothly dropping the raw material in the charge tube 21 when the bottom lid 23 is opened.

  On the other hand, the bottom plate portion 23b is formed of a material such as graphite, molybdenum, or tungsten having higher heat resistance than the cone portion 23a. Thus, the bottom lid 23 has not only the cone portion 23a but also the bottom plate portion 23b, and the bottom plate portion 23b is made of a material having high heat resistance, so that overheating of the cone portion 23a can be suppressed and thermal deformation can be prevented. . Further, it is possible to prevent the raw material from being melted in the charge tube 21.

  The shaft 24 is a member for raising and lowering the bottom lid 23, passes through the guide tube 25, extends in the vertical direction, and is connected to the upper end of the bottom lid 23. A head portion 24a is provided at the lower end of the shaft 24, and the diameter of the head portion 24a is larger than the diameter of a through hole 23c (see FIG. 8) provided at the upper end of the cone portion 23a of the bottom lid 23. The head portion 24a protruding downward from the hole 23c is engaged with the cone portion 23a. In addition, a vertical movable space of the head portion 24 a is secured inside the bottom cover 23, and there is play in the vertical movement of the bottom cover 23 with respect to the shaft 24. For this reason, the bottom lid 23 cannot move downward from the head portion 24a, but can move upward from the head 24a.

  The method for fixing the bottom plate portion 23b to the cone portion 23a is not particularly limited. For example, the bottom plate portion 23b may be fitted to a flange provided on the cone portion 23a side, or may be fixed by screwing. . In the case of fixing by screwing, for example, a through hole may be provided in the center of the bottom plate portion 23b, the shaft 24 may be passed through the through hole, and a nut may be fastened to the lower end of the shaft 24 via a washer.

  The guide tube 25 is provided to prevent the shaft 24 from coming into contact with the silicon raw material S in the charge tube 21. The guide tube 25 is made of quartz glass similarly to the charge tube 21 and the cone portion 23a, and the lower end thereof is connected to the upper end portion of the cone portion 23a, and the guide tube 25 is integrated with the cone portion 23a. The upper end portion of the guide tube 25 passes through the through hole 22a of the flange member 22 and protrudes upward from the flange member 22. The protruding amount is a protruding state even when the bottom lid 23 is lowered to the lowest position. Is to the extent that is maintained.

  Next, a silicon material recharging method and melting method using the recharging apparatus 20 will be described.

  3 to 6 are schematic cross-sectional views for explaining a silicon material recharging step and a melting step using the recharging device 20.

  As shown in FIG. 3, in the silicon material recharging step, first, the recharging device 20 containing the silicon material S is connected to the tip of the wire 17 of the silicon single crystal manufacturing device 1 and installed in the pull chamber 10b. The upper end of the shaft 24 of the recharging device 20 is connected to the tip of the wire 17. As a result, the recharge device 20 is disposed above the quartz crucible 12.

  Next, as shown in FIG. 4, the wire 17 is lowered to lower the recharge device 20. When the recharge device 20 is lowered for a while, the flange member 22 comes into contact with the locking piece 10e in the pull chamber 10b, and further lowering of the charge tube 21 is restricted. At this time, the vertical position of the lower end of the recharge device 20 is substantially the same as or lower than the lower end of the heat shield 16.

  Next, as shown in FIG. 5, the shaft 24 is lowered by further lowering the wire 17 in a state where the lowering of the charge tube 21 is restricted, and due to the weight of the silicon raw material S and the guide tube 25 and the weight of the bottom lid 23. The bottom cover 23 is lowered together with the shaft 24, whereby the lower end opening 21b of the charge tube 21 is opened and the silicon raw material S is dropped. Since the inner bottom surface of the bottom cover 23 is a conical inclined surface, the silicon raw material S falls smoothly without being caught by the bottom cover 23 and is put into the quartz crucible 12. Further, when the silicon raw material S is recharged, the lower end of the charge tube 21, that is, the lower end opening 21 b of the charge tube 21 is positioned substantially the same as or below the lower end of the heat shield 16. There is no collision, and damage to the heat shield 16 can be avoided.

  Thereafter, as shown in FIG. 6, the solid material recharged in the quartz crucible 12 is heated by the heater 15 to be melted. At this time, the recharge device 20 is placed in the main chamber 10a without being taken out, and the silicon raw material S in the quartz crucible 12 is melted while the bottom cover 23 is lowered, so that the bottom cover 23 is a so-called melt cover. Can function as.

  The height of the charge tube 21 and the bottom lid 23 in the raw material melting step may be the same height as at the time of the raw material recharge, or may be a different height. Therefore, for example, the raw material melting step may be performed after the charge tube 21 and the bottom cover 23 are pulled upward from the raw material recharge time. For example, by keeping the bottom lid 23 at the height of the lower end of the heat shield 16 while the bottom lid 23 is open, the heat retaining property of the silicon raw material in the quartz crucible 12 can be further enhanced.

  Thus, in the raw material melting step, the heat retention in the quartz crucible 12 is increased by using the bottom lid 23 as a melt lid, so that the heating efficiency of the silicon raw material S by the heater 15 can be increased, and the power consumption when the raw material is melted. Can be suppressed. Further, the cone portion 23a constituting the inner bottom surface of the bottom lid 23 is made of quartz, whereas the bottom plate portion 23b constituting the outer side surface of the bottom lid 23 is made of a material having higher heat resistance than the cone portion 23a. The overheating of the cone part 23a can be suppressed. Therefore, the bottom lid 23 can be used not only as a lid for the recharge device 20 but also as a melt lid, and the cone portion 23a is thermally deformed or silicon fine powder remaining on the surface of the cone portion 23a is melted and fixed. Therefore, it is possible to prevent a situation in which the degree of closing of the bottom lid 23 is deteriorated.

  FIGS. 7A to 7C are graphs showing simulation results of power consumption for one recharge raw material. The horizontal axis represents time (hr) and the vertical axis represents total power (kW). . This simulation was performed using simulation software “CGSim”.

  As shown in FIG. 7A, when no recharge device and melt lid are used, the power consumption per unit time (1 hr) is 220 kW, and the total power consumption (integrated value) for 5 hours is 1100 kW. Become.

  In addition, as shown in FIG. 7B, when the conventional recharge device and the melt lid are replaced and used, a setup loss occurs when the recharge device is replaced with the melt lid, and power is reduced during this period. The effect is not obtained. However, after replacing the melt lid, the power can be reduced, and the total power consumption (integrated value) for 5 hours is 1015 kW. That is, a total power reduction effect of about 9% can be expected as compared with the case where no recharge device and melt lid are used.

  On the other hand, as shown in FIG. 7C, when the replacement work from the recharge device to the melt lid is made unnecessary by using the recharge device according to the present invention, the power loss is reduced by 1.5 hours by eliminating the setup loss. An effect is obtained. And since the bottom cover 23 of the recharge apparatus 20 plays the role of a melt cover after charging the raw materials, the total power consumption (integrated value) for 5 hours is 974 kW. That is, a total power reduction effect of 13% can be expected compared to the case where no recharge device and melt lid are used, and a power reduction effect of 4% is expected compared to the case where the recharge device is replaced with a melt lid. Can do. If the number of recharges is 4, the setup loss for 6 hours is eliminated, and the effect becomes more remarkable as the number of recharges increases.

  FIGS. 8A to 8D are cross-sectional views showing variations of the structure of the bottom cover 23 of the recharging device 20.

  The bottom lid 23 shown in FIG. 8 (a) has the hollow structure shown in FIG. 2, and the hollow portion 23e of the bottom lid 23 surrounded by the cone portion 23a and the bottom plate portion 23b constitutes a cavity. Yes. In addition, the hollow part 23e of the bottom cover 23 is an area | region except the movable space of the up-down direction of the head part 24a (refer FIG. 2) of the shaft 24 among the insides of the bottom cover 23. FIG. The cone portion 23a is made of quartz glass, and a through hole 23c for engaging the head portion 24a is provided at the upper end portion thereof. The bottom plate part 23b is made of a material such as graphite, molybdenum or tungsten, which has higher heat resistance than the cone part 23a. Therefore, the cone part 23a can be protected from heat.

  As shown in FIG. 8B, the hollow portion 23e of the bottom lid 23 may be filled with carbon fibers 23f as a heat insulating material. By filling the hollow portion 23e with the carbon fiber 23f, the temperature of the cone portion 23a can be lowered. A material other than carbon fiber may be used as the heat insulating material, and in the case of the same material as the bottom plate portion 23b, the bottom plate portion 23b and the heat insulating material may be integrated. For example, when the bottom plate portion 23b is graphite, the filler may be graphite, or molybdenum or tungsten. Further, when the bottom plate portion is molybdenum, the heat insulating material may be molybdenum, or may be graphite or tungsten.

  As shown in FIG. 8C, the hollow portion 23e of the bottom lid 23 may be provided with a multilayer structure in which heat insulating material layers 23g and air layers 23h are alternately stacked. In this case, the material of the heat insulating material layer 23g is, for example, graphite, molybdenum, or tungsten. According to this structure, the temperature of both the baseplate part 23b and the cone part 23a can be lowered | hung.

  As shown in FIG. 8D, the hollow portion 23e of the bottom lid 23 may be provided with a multilayer structure in which two types of heat insulating material layers 23g and 23i are alternately stacked. The material of one heat insulating material layer 23g is, for example, graphite, and the material of the other heat insulating material layer 23i is molybdenum or tungsten. According to this configuration, the temperature of both the bottom plate portion 23b and the cone portion 23a can be lowered similarly to the structure shown in FIG.

  As described above, the recharge apparatus 20 according to the present embodiment has a quartz base 23 having a bottom lid 23 that opens and closes the lower end opening of the charge tube 21 and is attached to the bottom of the cone 23a. Since it is comprised with the part 23b, the heat resistance of the bottom cover 23 can be improved, ensuring the contamination prevention of the silicon raw material accommodated in the charge tube 21, and the ease of taking out. Therefore, the bottom lid 23 can be used as a melt lid at the time of raw material melting.

  In the silicon raw material melting method according to the present embodiment, after the silicon raw material is recharged into the quartz crucible 12 using the recharging device 20, the bottom lid 23 of the recharging device 20 is used as a melt lid in the recharging raw material melting step. In addition, since the raw material is heated, the time required for the changeover from the recharge device to the melt lid (vacuum release, recharge device removal, melt lid attachment, and evacuation) and loss of power consumption can be reduced. Accordingly, the heating efficiency of the raw material can be increased to reduce power consumption, and the raw material melting time can also be shortened.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, in the above embodiment, the lowering of the charge pipe 21 is restricted by the flange member 22 engaging with the locking piece 10e in the pull chamber 10b, and the bottom lid 23 is lowered by further lowering the shaft 14 in this state. However, the opening / closing mechanism of the bottom lid 23 is not particularly limited, and various structures can be employed.

  In the silicon raw material melting process using the bottom cover of the recharge device, the effect of the difference in the structure of the bottom cover on the input power was evaluated by simulation. The simulation software “CGSim” described above was used for the simulation. The structure of the bottom lid to be evaluated is as follows.

  First, Comparative Example 1 is a case where no melt lid is used. In the bottom cover of Comparative Example 2, the cone part and the bottom plate part of the bottom cover are made of graphite, and the inside of the bottom cover is filled with a fiber heat insulating material. In other words, this bottom cover is entirely made of graphite.

  In each of Examples 1 to 6, the cone portion of the bottom lid is made of quartz glass, but the bottom plate portion of the bottom lid or the structure inside the bottom lid is different from each other. For example, the bottom plate portions of Examples 1 and 2 are made of graphite, and the bottom plate portions of Examples 3 to 6 are made of molybdenum. The inside of the bottom lids of Examples 1 and 3 are hollow (no filling material), and the inside of the bottom lids of Examples 2 and 4 is filled with a fiber heat insulating material. Further, the inside of the bottom lid of Example 5 is composed of a multilayer structure in which molybdenum plates and air layers are alternately laminated, and the inside of the bottom lid of Example 6 is a multilayer in which molybdenum plates and graphite plates are alternately laminated. Consists of a structure.

  In the simulation, a recharge apparatus was installed in the silicon single crystal manufacturing apparatus shown in FIG. 1, and 480 kg of silicon raw material was charged in the quartz crucible. The furnace pressure was 40 Torr, the argon gas flow rate was 250 ml / min, and the gas flow was set to a laminar flow model. As a temperature control point, a silicon melting point of 1412 ° C. was set 1 mm below the melt surface center. Under such conditions, the power required to melt the raw material by increasing the power of the heater was obtained. The results are shown in Table 1.

  As is clear from Table 1, in Comparative Example 1, the electric power necessary for melting the raw material in the quartz crucible was 112.5 kW, whereas in Comparative Example 2, it was 80.4 kW, about 30%. It was confirmed that there was a power reduction effect. However, Comparative Example 2 has a practical problem because the entire bottom lid is made of graphite.

  In Examples 1 to 6, as in Comparative Example 2, the effect of reducing the power could be confirmed. Among these, the electric power of Examples 1, 2, 3, and 4 was 81.4 kW, 79.7 kW, 80.3 kW, and 79.6 kW, respectively, and all were the electric power reduction effect of the same level as the comparative example 2. On the other hand, the electric power of Example 5 is 74.3 kW, and the electric power of Example 6 is 72.5 kW. In the case where the inside of the bottom cover has a multilayer structure, the heat retention is further improved as compared with Examples 1 to 4. As a result, it was found that there is a high power reduction effect.

DESCRIPTION OF SYMBOLS 1 Silicon single crystal manufacturing apparatus 2 Silicon single crystal 3 Silicon melt 10 Chamber 10a Main chamber 10b Pull chamber 10c Gas inlet 10d Gas exhaust 10e Locking piece 11 Heat insulating material 12 Quartz crucible 13 Graphite crucible 14 Shaft 15 Heater 16 Heat shield Body 16a Opening 17 Wire 18 Wire winding mechanism 19 Shaft drive mechanism 20 Recharging device 21 Charge pipe 21a Charge pipe upper end opening 21b Charge pipe lower end opening 22 Flange member 22a Flange member through hole 23 Bottom lid 23a Cone 23b Bottom plate part 23c Cone through hole 23e Hollow part 23f Carbon fiber 23g Heat insulation material layer 23h Air layer 23i Heat insulation material layer 24 Shaft 24a Shaft head part 25 Guide tube S Silicon raw material

Claims (6)

A method of melting silicon raw material using a recharge device,
The recharging device is:
A charge tube containing silicon raw material;
A bottom lid that opens and closes a lower end opening of the charge tube;
A shaft that supports the bottom lid so as to be movable up and down;
The bottom cover is made of quartz glass, and is formed of a cone-shaped cone portion constituting the inner bottom surface of the charge tube, and a material having higher heat resistance than the cone portion, and is a flat portion constituting the outer bottom surface of the charge tube. Including a bottom plate part,
The melting method is:
Placing the recharge device containing the silicon raw material above the quartz crucible in the chamber;
Lowering the bottom lid that closes the lower end opening of the charge tube of the recharge device to open the lower end opening, dropping the silicon material in the charge tube, and dropping the silicon material into the quartz crucible Recharging
Melting the silicon material, wherein the recharging device is installed in the chamber and the silicon material in the quartz crucible is heated and melted with a heater while the bottom cover is lowered. Method. The method for melting a silicon raw material according to claim 1, wherein the bottom plate portion includes at least one material selected from graphite, tungsten, and molybdenum. The silicon raw material melting method according to claim 1 or 2, wherein the inside of the bottom lid surrounded by the cone portion and the bottom plate portion is a cavity. The silicon raw material melting method according to claim 1 or 2, wherein carbon fiber is filled in the bottom lid surrounded by the cone portion and the bottom plate portion. In the inside of the bottom lid surrounded by the cone portion and the bottom plate portion is provided a multilayer structure in which heat insulating material layers and hollow layers are alternately laminated,
The method for melting a silicon raw material according to claim 1, wherein the heat insulating material layer includes at least one material selected from graphite, tungsten, and molybdenum. A multilayer structure in which a first heat insulating material layer and a second heat insulating material layer are alternately stacked is provided inside the bottom cover surrounded by the cone portion and the bottom plate portion,
The first heat insulating material layer includes at least one material selected from graphite, tungsten and molybdenum,
The method for melting a silicon raw material according to claim 1 or 2, wherein the second heat insulating material layer is made of carbon fiber.